This invention relates to an adsorption apparatus wherein a gas mixture is subjected to adsorption and subsequent separation into its components by pressure swing adsorption, which will be hereinunder referred to as PSA, and particularly to an adsorption apparatus wherein the heat of adsorption generated is effectively recovered to enhance the desorption rate from the adsorbent packed therein and also the noise caused by a gas flow in PSA operation is considerably abated by the adsorbent bed.
In the conventional PSA adsorption technique for producing an oxygen-enriched gas from an oxygen-containing gas, for example, air, using a bed of zeolite molecular sieve packed as an adsorbent in an adsorption apparatus (U.S. Pat. Nos. 3,923,479, and 3,738,087), the air is subjected to selective adsorption of nitrogen on the bed of zeolite molecular sieve by trapping the nitrogen in the pores of the molecular sieve, while the heat of adsorption of about 0.2 Kcal per 1 Nl of the adsorbed gas is generated. The unadsorbed gas, that is, oxygen-enriched gas, moves through the bed toward the outlet of the apparatus, while being heated by the generated heat of adsorption, that is, the unadsorbed gas has an elevated temperature by the heating with the generated heat of adsorption and carries away the heat to the outside of the adsorption apparatus.
On the other hand, when the adsorbed nitrogen is desorbed by reducing the pressure to the lower level than that of adsorption, an endothermic phenomenon takes place, and the temperature of the adsorbent bed is lowered by adiabatic cooling. That is, the adsorbent bed portion near the inlet of the adsorption apparatus is inevitably cooled down to a lower temperature. If the adsorbent bed is cooled down to a temperature too low, the moisture and CO.sub.2 in the desorbing gas which have a strong affinity toward the adsorbent are firmly trapped in the adsorbent, reducing the separation efficiency between the nitrogen and the oxygen.
When the adsorption and desorption are carried out repeatedly, the adsorbent bed will finally have such a temperature distribution as given by curve "Conventional" in FIG. 1 with a considerable temperature difference between the inlet side and the outlet side of the adsorbent bed.
Moreover, in the conventional PSA technique, a large amount of the unadsorbed gas, for example, oxygen-enriched gas, leaving the adsorption apparatus is passed through an outside piping with a considerably smaller cross-sectional area than that of the adsorption apparatus, and thus the flow rate of the unadsorbed gas passing through the piping becomes so high while the gas pressure is widely and frequently changed during the adsorption and desorption steps in the PSA operation that a high level noise occurs outside the adsorption apparatus.